Products such as insulation and structural products have been made from mineral fibers, particularly glass fibers, for some time. A well-known rotary process of making mineral fibers includes centrifuging molten mineral material through small orifices to form mineral fibers. Molten mineral material is supplied to a rotating annular spinner. The spinner has a peripheral wall with a plurality of small orifices. The spinner is heated to keep the mineral material in the molten state. As the spinner is rotated, centrifugal force moves the molten mineral material against the peripheral wall. The molten mineral material is centrifuged from the rotating spinner and forced through the orifices in the peripheral wall of the spinner to form mineral fibers. This process provides an efficient way of producing mineral fibers at high production rates.
Many uses for polymeric fibers, such as polymer fibers, have been developed because of the desirable qualities of organic fibers. For example, polymeric fibers can be used to produce insulation products having a great degree of flexibility. Polymeric fibers are more resistant to breaking under deflection than glass fibers in typical insulation products. These polymeric fiber insulation products also have better handleability than glass fibers because they do not irritate the skin. Polymeric fibers can be used in a wide range of applications including sorbent materials, thermal and acoustical insulation, filters, and stuffing/padding materials.
To take advantage of the proven efficiency and high production rates of the rotary process of producing mineral fibers, it would be desirable to be able to produce organic fibers, including polymer fibers, in a similar way. But molten polymeric material has different physical properties from a molten mineral material. Some molten polymeric materials have decomposition temperatures that limit the upper spinner temperature. As a result, these materials are too viscous for producing fibers by a rotary process at the temperatures where they can be processed. For example, polypropylene with a melt flow index below 35 is unsuitable for a rotary fiberizing process. It would be possible to provide a polymeric material having a higher melt flow index. However, the cost of such a material would be significantly higher. Therefore, it would be desirable to be able to use a rotary process to make fibers from polymeric materials having a low melt flow index.